Development of Motion Estimation Method of Porpoising for High Speed Planing Craft with Outboard Engine

Abstract

The purpose of this study is to develop a simulation method of porpoising for real scaled planing craft with outboard engine. At first, in order to check the conditions where porpoising occurs, a free running attitude towing tank test is carried out. In the test,longitudinal position of the center of gravity and ship's weight are systematically changed. And in order to investigate the effects of outboard engine on occurrence of porpoising, the same test is also carried out for the models with and without lower hull of outboard engine. From the measured results, it is found that lower hull of outboard engine can reduce the occurrence of porpoising.In the simulation, measured three components hydrodynamic forces acting on fully captured model are used. In order to simulate porpoising for real scaled planing craft, the scale effects on the hydrodynamic forces are taken into account. As the results, it is found that the condition of porpoising occurrence for a real scaled craft is slightly different from the model scaled craft, because of difference of running attitude between them affected scale effects. Finally, a simulation method of porpoising for real scaled planing craft is developed and a method for avoiding porpoising is proposed.